The invention relates to a pulse generator with a switchable output frequency and a selectable clock pulse ratio with the different output frequencies from a comparator, a voltage divider being connected to its input as well as a capacitor which is chargeable by the supply voltage, whereby an output signal dependent on the ratio of the input voltages arises at the output of the comparator, as well as having two transistors connected to the output of the comparator, whereby the divider ratio of the voltage divider is adjusted so as to determine the frequency via one transistor, while the other represents a discharge current path for the capacitor.
Pulse generating circuits are already known in which two voltages are compared in a comparator. One of the two input voltages constantly changes until it reaches the value of the other fixed input voltage and thus brings about a change in the output signal from the comparator.